In order to make a foot orthotic, an impression of a foot is required. There are numerous ways to take an impression of a foot for the manufacture of orthotics and the most common is to have a patient lay on their back or stomach so as to be either in the supine or prone position. A plaster bandage is then wrapped over the sole and sides of the foot and held in position whilst pushing against the fourth and fifth toes until a resistance is felt. This is considered to be the “neutral” position defined as the foot being in line with the leg and talus bone is centered between the lateral and medial malleolus. This is presumed to be the best and most functional position for the foot to be in and is maintained in that position until the plaster is dried. Once dry, the cast is removed from the foot and the process is repeated for the other foot.
In most cases it is known that there will be a difference between the forefoot to rear foot relationship in the cast. Some prior methods were employed on the basis that if the rear foot of the negative cast is balanced with the forefoot so that the rear foot is vertical this would be the best position for the foot to be in. By placing a wedge under the medial or lateral aspect of the forefoot and pouring the negative cast in this balanced position achieves this. An orthotic is made from the mould of this new balanced position that will promote the foot to sit in the same position when the feet are bearing weight on the orthotics. Unfortunately, this method is problematic in that the balanced positive model of the cast has to be balanced and modified to try and represent what the foot would look like in a corrected weight bearing position.
In its simplest form, bisection of the balanced positive model is made corresponding to the first and fifth metatarsals with nails hammered vertically into these marks until level with the top of the cast. A forefoot block is made with plaster and cut to the proximal edge of the nails. The gap created from the medial side of the forefoot block must be filled and modified with plaster which tapers off gradually to nothing when it reaches the medial cuneiform and navicular.
It will be appreciated that the height and shape of the medial longitudinal arch of a foot is very subjective in characterization and will change, depending on the particular clinician, balancing and cast modification instructions, with the clinician's individual interpretation of those instructions and the variations of the modification between technicians. The next step in the process is to add plaster to the lateral side of the cast which tapers at the back of the heel. This is done to compensate for the fatty tissue in the foot spreading when in a (corrected) weight bearing position. A nail is then added to the central side of the heel with a predetermined length, preferably between 2 mm to 8 mm depending on how much fatty tissue expansion is required. Typically, 3 to 4 mm is considered normal exposure for the nail in the central lateral side of the heel cast.
Once the nails are in position, plaster is added to the lateral side of the cast and rounded off so that there are no sharp edges. This can be done by hand or scraped back to the desired shape when the plaster has set. Unfortunately, there are many variables involved with this common process. The first major variable is that the original process of taking the cast occurs while the foot is not in a weight bearing position. It is known that there is significant variation in the rear foot bisection of a non-weight bearing cast which is not only between practitioners/clinicians but even when a single practitioner/clinician takes the same casts several times.
It is the genesis of this invention to provide a foot alignment tool that will address the disadvantages of the prior art, or to provide a useful alternative.